Hemoglobin present in red blood cells can be glycated by the non-enzymatic addition of a glucose molecule to the amino terminus of the β-chain of the hemoglobin. Once a hemoglobin molecule is glycated, it remains glycated, and an accumulation of glycated hemoglobin within a red cell reflects the average level of glucose to which the cell has been exposed during its life cycle. The level of glycated hemoglobin present in an individual's blood is thus proportional to the level of glucose in the blood, and is an indicator of the individual's mean daily blood glucose concentration over the previous four weeks to three months.
Numerous methods exist for determining the level of glycated hemoglobin in human blood, most of which involve calculating the relative amount of glycated hemoglobin A (HbA1c) present in the blood, due to the fact that hemoglobin A (HbA) is the major form of hemoglobin present in human blood. Techniques such as high performance liquid chromatography and immunoaffinity selection are used in such methods, which take advantage of physical and/or chemical properties of glycated hemoglobin A that distinguish it from other forms of hemoglobin present in the blood.
Variant forms of hemoglobin exist, however, such as hemoglobin S (HbS) and hemoglobin C (HbC), which differ from hemoglobin A at the amino acid residue at position six of the hemoglobin β-chain. The hemoglobin S and hemoglobin C forms of hemoglobin can be glycated, and glycated hemoglobin S and hemoglobin C have been shown to interfere with most of the current methods for quantitating glycated human hemoglobin, causing up to a 40% elevation in the results. A need therefore exists for methods for detecting glycated human hemoglobin that are not subject to interference caused by hemoglobin variants.